When dating an older man?

I am dating a man that is 15 years older than me. I didn't expect to start liking him, but now I do. When we first started everything, we both admittedly were bad at the whole relationship thing. Now we have came to the conclusion that we don't want to see others and be exclusive, but he doesn't want me to refer to him as my boyfriend. Is he just using lines on me, or is he scared to be in a relationship? I spend nearly every night at his house, so I know he's not doing anything with anyone else. I think that he may be thinking that he can't keep my attention because of the age difference but that is not even close to the truth. What should I do?